string/FreeBSD/strerror.3

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  32 .\"     @(#)strerror.3  8.1 (Berkeley) 6/9/93
  33 .\" $FreeBSD: src/lib/libc/string/strerror.3,v 1.24 2007/01/09 00:28:12 imp Exp $
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  35 .Dd October 12, 2004
  36 .Dt STRERROR 3
  37 .Os
  38 .Sh NAME
  39 .Nm perror ,
  40 .Nm strerror ,
  41 .Nm strerror_r ,
  42 .Nm sys_errlist ,
  43 .Nm sys_nerr
  44 .Nd system error messages
  45 .Sh LIBRARY
  46 .Lb libc
  47 .Sh SYNOPSIS
  48 .In stdio.h
  49 .Ft void
  50 .Fo perror
  51 .Fa "const char *s"
  52 .Fc
  53 .Vt extern const char * const sys_errlist[] ;
  54 .Vt extern const int sys_nerr ;
  55 .In string.h
  56 .Ft "char *"
  57 .Fo strerror
  58 .Fa "int errnum"
  59 .Fc
  60 .Ft int
  61 .Fo strerror_r
  62 .Fa "int errnum"
  63 .Fa "char *strerrbuf"
  64 .Fa "size_t buflen"
  65 .Fc
  66 .Sh DESCRIPTION
  67 The
  68 .Fn strerror ,
  69 .Fn strerror_r ,
  70 and
  71 .Fn perror
  72 functions look up the error message string corresponding to an
  73 error number.
  74 .Pp
  75 The
  76 .Fn strerror
  77 function accepts an error number argument
  78 .Fa errnum
  79 and returns a pointer to the corresponding
  80 message string.
  81 .Pp
  82 The
  83 .Fn strerror_r
  84 function renders the same result into
  85 .Fa strerrbuf
  86 for a maximum of
  87 .Fa buflen
  88 characters and returns 0 upon success.
  89 .Pp
  90 The
  91 .Fn perror
  92 function finds the error message corresponding to the current
  93 value of the global variable
  94 .Va errno
  95 .Pq Xr intro 2
  96 and writes it, followed by a newline, to the
  97 standard error file descriptor.
  98 If the argument
  99 .Fa s
 100 is
 101 .Pf non- Dv NULL
 102 and does not point to the null character,
 103 this string is prepended to the message
 104 string and separated from it by
 105 a colon and space
 106 .Pq Dq Li ":\ " ;
 107 otherwise, only the error message string is printed.
 108 .Pp
 109 If the error number is not recognized, these functions return an error message
 110 string containing
 111 .Dq Li "Unknown error:\ "
 112 followed by the error number in decimal.
 113 The
 114 .Fn strerror
 115 and
 116 .Fn strerror_r
 117 functions return
 118 .Er EINVAL
 119 as a warning.
 120 Error numbers recognized by this implementation fall in
 121 the range 0 <=
 122 .Fa errnum
 123 <
 124 .Fa sys_nerr .
 125 .Pp
 126 If insufficient storage is provided in
 127 .Fa strerrbuf
 128 (as specified in
 129 .Fa buflen )
 130 to contain the error string,
 131 .Fn strerror_r
 132 returns
 133 .Er ERANGE
 134 and
 135 .Fa strerrbuf
 136 will contain an error message that has been truncated and
 137 .Dv NUL
 138 terminated to fit the length specified by
 139 .Fa buflen .
 140 .Pp
 141 The message strings can be accessed directly using the external
 142 array
 143 .Va sys_errlist .
 144 The external value
 145 .Va sys_nerr
 146 contains a count of the messages in
 147 .Va sys_errlist .
 148 The use of these variables is deprecated;
 149 .Fn strerror
 150 or
 151 .Fn strerror_r
 152 should be used instead.
 153 .Sh SEE ALSO
 154 .Xr intro 2 ,
 155 .Xr psignal 3
 156 .Sh STANDARDS
 157 The
 158 .Fn perror
 159 and
 160 .Fn strerror
 161 functions conform to
 162 .St -isoC-99 .
 163 The
 164 .Fn strerror_r
 165 function conforms to
 166 .St -p1003.1-2001 .
 167 .Sh HISTORY
 168 The
 169 .Fn strerror
 170 and
 171 .Fn perror
 172 functions first appeared in
 173 .Bx 4.4 .
 174 The
 175 .Fn strerror_r
 176 function was implemented in
 177 .Fx 4.4
 178 by
 179 .An Wes Peters Aq wes@FreeBSD.org .
 180 .Sh BUGS
 181 For unknown error numbers, the
 182 .Fn strerror
 183 function will return its result in a static buffer which
 184 may be overwritten by subsequent calls.
 185 .Pp
 186 The return type for
 187 .Fn strerror
 188 is missing a type-qualifier; it should actually be
 189 .Vt const char * .
 190 .Pp
 191 Programs that use the deprecated
 192 .Va sys_errlist
 193 variable often fail to compile because they declare it
 194 inconsistently.